An Evaluation of the Fracture Resistance of Teeth with Simulated External Cervical Resorption Cavities Categorized Using Three-Dimensional Classification

(1) Background: External cervical resorption causes dental hard tissue destruction that may reduce the fracture resistance of affected teeth. By using a compressive strength test, this study aimed to evaluate the fracture resistance of teeth with simulated external cervical resorption cavities that have different three-dimensional classifications. (2) Methods: In total, 170 teeth with simulated external cervical resorptions were divided into 16 experimental groups (n = 10) and 1 control group (n = 10) based on the three-dimensional classification: 1Ap, 1Bp, 1Cp, 1Dp, 2Ap, 2Bp, 2Cp, 2Dp, 3Ap, 3Bp, 3Cp, 3Dp, 4Ap, 4Bp, 4Cp, 4Dp and a control group. Defects were restored with mineral trioxide aggregate. The fracture resistances of the samples were statistically analyzed using two-way repeated ANOVA and the Bonferroni correction for multiple comparisons at a significance level of p < 0.05. (3) Results: The lowest resistance to fracture was observed in samples with vertical height level “4” and circumferential spread of “D” (p < 0.001). In the groups with circumferential spreads “B”, “C” and “D”, there were significant differences between the samples with vertical height levels “1”, “2”, “3” and “4” regarding fracture resistance (p < 0.001). (4) Conclusions: The circumferential spread and vertical height of the external cervical resorption influenced the fracture resistance of the affected teeth.